1. Field of the Invention
The present invention relates to a window plate made of synthetic resins and adapted for use in the automobile vehicles or the like, and more particularly relates to a window plate made of synthetic resins to have an antifogging property, as well as a method of making the window plate.
2. Prior Art
Many proposals have been made to substitute plastics boards for the classical glass windows, so as to render the automobile bodies lighter in weight. On the other hand, the problem of an atmospheric vapor condensing to fog the windows and to lower the visibility thereof has been reported, whether the windows are made of glass or plastics. Certain plastics window plates of a double-stratified structure consisting of a plastics base and a resin film bonded thereto were developed to resolve this problem. In connection with the plastic window, a pattern of electrically conductive heating wire has been proposed to be previously printed on the resin film.
An example of such proposals is disclosed in the Japanese Unexamined Patent Publication No. Hei. 6-170883, wherein a resin film of a window shape and having the pattern of heating wire printed thereon is inserted in an injection mold. Another resin injected into this mold will form a base integral with the inserted resin film to provide a two-stratified window plate. The printing of the pattern of heating wire can easily be done onto the thin, flat and transparent resin film, and such film will readily be disposed in the mold so as to fit on a curved wall of its cavity. Thus, plastics window plates may be produced efficiently to be of any desired accurate shape and dimension as usual in the injection molding. The method proposed in the Publication No. 6-170883 can produce the window plate of either type shown in FIG. 9A or 9B, depending on whether a front side or a rear side of the resin film 21 is in contact with the cavity wall. In one type 23 of the window plate, the film's side 21a having the printed pattern of heating wire 22 is exposed to the outside. In the other type 25, said side 21a merges with the plastics base 24 and is not exposed.
It is however noted that both the types 23 and 25 are not necessarily an ideal product. In a case wherein the window plate 23 has the heating wire 22 exposed as shown in FIG. 9A, the thickness of the wire amounting to several tens .mu.m will cause a noticeable undulation in the film 21 due to the pressure and heat of the resin injected to form the plastics base. Such an undulation will not only spoil the appearance but also distort an image seen through this window plate. In another case wherein the window plate 25 has the heating wire 22 not exposed as shown in FIG. 9B, the surface unevenness of resin film 21 will be diminished by the plastic base so that the window plate has smooth major surfaces. However, an electric wiring to the embedded heating wire 22 would not be possible unless certain special after-treatments are done of this window plate.